1. Field of the Invention
The present invention relates to a camera diaphragm control method.
2. Description of the Prior Art
Conventional diaphragm control has thus far been accomplished such that a diaphragm member begins to operate when the camera diaphragm size is determined and set, and simultaneously the amount of diaphragm member movement is detected by, for example, counting a series of pulses. The diaphragm operation stopper is then actuated and the diaphragm member strikes the stopper, stopping its motion, when the diaphragm member reaches the point of prescribed diaphragm value (e.g., the proper number of pulses).
In the foregoing method, the diaphragm operation stopper begins its motion after the diaphragm member has reached the point of the prescribed diaphragm value; there is therefore inevitably a difference between the actual diaphragm opening and the prescribed amount thereof. This is never desirable because it leads to an error when the diaphragm is stopped down. To solve this, many methods have been adopted, such as ones in which the operational speed of the diaphragm operation stopper is increased or the operational speed of the diaphragm member is decreased. If the operational speed of the diaphragm operation stopper is increased, the kinetic energy of the relative members is increased and, when stopped in operation, significant noise and impact result thereby shortening the life of the members. If, on the other hand, the operational speed of the diaphragm member is decreased, a photographing opportunity is sometimes lost.
Moreover, to eliminate delays in the action of these operation members, a method has been devised wherein, for example, the diaphragm operation stopper is actuated before the diaphragm member reaches the point of prescribed diaphragm value (e.g., before two pulses are given). In this method, it is sufficient if the operational speed of the diaphragm member is predeterminately fixed; however, in practice, there are sizable variations in such speed, from which errors result.
Generally, the operational speed of a member is determined in accordance with the force imparted thereto and the inertia and friction of the member. With respect to a diaphragm operation stopper, the force thereon is generated by a spring or a solenoid. The effect of its inertia on its moving speed can be minimized once the shape and material of the member are determined, and the friction thereof will not appreciably fluctuate if the member is assembled and shakedown-tested once. The diaphragm operation stopper will always function at a stable speed with little variation.
On the other hand, the force and inertia associated with a diaphragm member of an interchangeable lens significantly fluctuate so that its speed is sharply affected by the accelerated velocity at its initial stage of operation (where the diaphragm is fully opened) and at the point in time at which the diaphragm is stopped down.